Among environmentally-friendly vehicles, a hybrid electric vehicle (HEV) is provided with an engine using fuel and a motor using battery power for generating power used for driving the vehicle, and travels in an electric vehicle (EV) mode in which only motor power is transmitted to driving wheels or in a hybrid electric vehicle (HEV) mode in which the combination of engine power and motor power is transmitted to the driving wheels in a parallel mode.
In addition to the engine and the motor (hereinafter, referred to as a ‘second motor’) for driving the vehicle, a motor (hereinafter, referred to as a ‘first motor’) for generating electric power, which produces electrical energy by being supplied with power from the engine, is additionally provided. Thus, when a state of charge (SOC), which represents a charge amount of the battery, decreases to a predetermined level or lower, the first motor is operated by engine power so as to generate electric power for charging the battery, and the second motor is operated by battery power so as to allow the vehicle to travel with the power from the second motor [series mode], thereby increasing a distance that the vehicle can travel.
A plug-in hybrid electric vehicle (PHEV) can charge the battery by using a commercial electric power source, and travels optionally in a charge depleting (CD) mode and in a charge sustaining (CS) mode in accordance with the SOC of the battery.
The CD mode means a section of the EV mode where the vehicle travels only by the second motor driven by the battery power, and since the SOC of the battery is sufficient and available electric power is high, the vehicle travels only by using power from the second motor in most sections except for a special situation.
The CS mode means a section where the vehicle travels with an appropriate combination of power from the engine and power from the second motor like in the HEV mode (parallel mode) after using a predetermined amount of the battery power, or a section where the vehicle travels with power from the second motor like in the series mode while allowing the first motor to generate electric power by using engine power and allowing the battery to be charged.
Since in the CS mode, the SOC of the battery is not sufficient and available electric power is relatively low, the vehicle travels with a combination of engine power and motor power, or travels with motor power while using engine power to generate electric power and then charging the battery, thereby improving fuel efficiency, increasing a distance that the vehicle can travel, and maintaining an appropriate SOC of the battery.
FIG. 10 is a view illustrating a state in which a plug-in hybrid electric vehicle (PHEV) travels in an EV mode, an engine 1 and a first motor (MG1) 2 for generating electric power are connected to each other so as to transmit power therebetween, and a second motor (MG2) 4 for driving the vehicle and a driving wheel are connected to each other so as to transmit power therebetween.
The first motor 2 and the second motor 4 are connected with a battery 6 via an inverter system 5 so as to charge and discharge the battery 6, and an engine clutch 3, which selectively transmits or shuts off engine power, is disposed at an output side of the engine 1.
As illustrated, when the vehicle travels in the EV mode, the second motor 4 is driven by electric power from the battery 6 in a state in which the engine clutch 3 is disengaged, thereby allowing the vehicle to travel only with power from the second motor.
When the vehicle travels in the series mode, the first motor 2 is operated by power from the engine 1 so as to generate electric power and charge the battery 6 in a state in which the engine clutch 3 is disengaged, and at the same time, the second motor 4 is driven by electric power from the battery 6, thereby allowing the vehicle to travel with power from the second motor.
When the vehicle travels in the parallel mode, power from the engine 1 and power from the second motor 4 are transmitted to the driving wheel 7 in a state in which the engine clutch 3 is engaged, thereby allowing the vehicle to travel.
However, the engine clutch 3 used for the system as illustrated in FIG. 10 has drawbacks in that production costs and material costs thereof are high, and a large amount of power loss occurs due to rotation of a clutch rotating element (a part that receives power from the second motor) at the output side even though the clutch rotating element is disengaged when the vehicle travels in the EV mode, which deteriorates traveling efficiency in the EV mode.
In the case of the system as illustrated in FIG. 10, the engine 1 has only one stationary gear stage, and thus, there is a limitation in the traveling efficiency in the parallel mode.
The above information disclosed in this Background section is only for enhancement of understanding the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.